Tank B contained 2 times as many guppies as Tank C. When 50% of the guppies in Tank B and 10% of the guppies in Tank C were transferred to Tank D, Tank D had 198 guppies, which was 20% more guppies than before. How many more guppies were there in Tank D than Tank C in the end?

	Tank B	Tank C	Tank D
Before	2 u	1 u	5x1.1 = 5.5 u
Change	- 1 u	- 0.1 u	+ 1x1.1 = + 1.1 u
After	1 u	0.9 u	6x1.1 = 6.6 u

Number of guppies that were transferred from Tank B to Tank D
= 50% x 2 u
= ⁵⁰₁₀₀ x 2 u
= 1 u

Number of guppies that were transferred from Tank C to Tank D
= 10% x 1 u
= ¹⁰₁₀₀ x 1 u
= 0.1 u

20% = ²⁰₁₀₀ = ¹₅

Some guppies from Tank B and Tank C were transferred to Tank D.  The total number of guppies transferred from Tank B and Tank C into Tank D is the same.

Total number of guppies transferred from Tank B and Tank C into Tank D
= 1 u + 0.1 u
= 1.1 u

6.6 u = 198

1 u = 198 ÷ 6.6 = 30

Number of more guppies in Tank D than Tank C
= 6.6 u - 0.9 u
= 5.7 u
= 5.7 x 30
= 171

Answer(s): 171